Vision performance standards in the United States, and around the world, rely on visual acuity testing that, in turn, relies on presenting a range of black letters on a white background to patients. Studies show that the test results can vary greatly based on the type of vision test used and the conditions in which the test is administered.
To ensure standardization, a number of recommended parameters for visual acuity testing have been established, including letter height, letter width, letter spacing, letter type, scoring procedures, testing distance and testing luminance. Clinicians, in general, have adopted these testing parameters. But, standardization of test lighting has not been adopted and this is an area of extreme need. Data shows that results of the acuity test vary greatly dependent on the testing light levels. It is well established that higher light levels produce significantly better vision results than lower light levels and that older patients are more affected by testing light levels than younger patients.
While the need for standardization has been recognized for some time, luminance standards have not heretofore been adopted by practicing eye doctors primarily because most eye doctors used the same type of vision testing equipment, which inherently created less variance due to the similarities of the devices. In addition, the required accuracy of vision testing was not such that differences in luminance levels between examination lanes or between eye clinics would create a problem for documenting the visual performance.
However, these two factors have now changed. Many eye doctors are no longer using the same types of devices for vision testing, greatly increasing the variability of luminance levels used between doctors. The projection systems that were common in the past have been replaced by computer displays that have widely varying luminance, and hence, the variability between test systems has increased substantially.
In addition, many new vision correction surgical techniques are being developed which are driving a need to improve the accuracy of vision test results in order to document the benefits of surgery and so that the outcomes of different types of procedures can be accurately compared. Further, United States government healthcare reimbursement agencies are moving to a system in which eye doctors will be reimbursed for services based on the quality of the visual outcomes related to treatment. This change in reimbursement strategies will by necessity require more accuracy in the measurement of visual acuity, since visual acuity is the primary outcome measure for the vast majority of eye treatments.
Finally, the computer display screen on which the test pattern is projected is often located at a place in the examination room that is difficult for personnel to access physically. For example, the screens are often placed high on a rear wall of a small examination room and viewed by the patient via one or more mirrors. Measuring the intensity of illumination at the screen requires the technician to use a stool or ladder to place a light meter on the screen in the region of the screen being used to display the test pattern. As a result, such calibration measurements are rarely made in practice.